1. Field of the Invention
This invention pertains to a laminated heated plate glass, especially for an airplane cockpit.
2. Description of the Related Art
An airplane window normally includes at least two sheets of structural glass connected to one another by a first intermediate layer made of transparent plastic, for example polyvinylbutyral (PVB) or of polyurethane, the sheet of structural glass which faces the external side of the cockpit being covered by at least one third sheet, made of tempered glass or glass reinforced chemically through the intermediary of another intermediate layer made of PVB or of polyurethane.
The third sheet and the second intermediate layer have dimensions which are reduced with respect to those of the two sheets of structural glass, so as to form on the latter a peripheral overlapping edge which is to be received in a rabbet of the cockpit.
In order that a plate glass of this type can be heated, it is known to place a network of thin, generally parallel conducting wires or an electrically conducting film between the first intermediate layer and the sheet of glass which is turned toward the outside, during fabrication, these components being connected to two current input strips or collectors which are connected to a source of current external to the plate glass.
Under normal conditions of use which prevail during flight, the plate glass is subjected to stresses due to pressure and temperature differences between the two sides of the plate glass, which generate shearing forces between the different layers of the plate glass and therefore relative displacement of the different components which comprise the laminated structure, and in particular displacement of the first intermediate layer and current input strips with respect to the wires. Due to this displacement, there can occur a rupture of the electric wires and therefore a disturbance in the temperature regulation of the plate glass. Short circuits and localized overheated spots can occur, possibly causing breakage of one or even both sheets of structural glass.